Add /proc/sys/vm/drop_node_caches

drop_node_caches allows the dropping of all pagecache for a certain node
in a NUMA system. Explicit clearing a node may often be desirable to get
consistent placement for the pages of an application.

This works by writing the node number for which to clear the pagecache
to /proc/sys/vm/drop_node_caches.

F.e. to clear the pagecache on node 3 do:

echo 3 >/proc/sys/vm/drop_node_caches

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.17-rc4-mm3/include/linux/swap.h
===================================================================
--- linux-2.6.17-rc4-mm3.orig/include/linux/swap.h	2006-05-23 15:10:22.012855010 -0700
+++ linux-2.6.17-rc4-mm3/include/linux/swap.h	2006-05-24 15:55:16.925742236 -0700
@@ -191,6 +191,7 @@ extern int remove_mapping(struct address
 extern int zone_reclaim_mode;
 extern int zone_reclaim_interval;
 extern int zone_reclaim(struct zone *, gfp_t, unsigned int);
+extern void drop_node_pagecache(int node);
 #else
 #define zone_reclaim_mode 0
 static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
Index: linux-2.6.17-rc4-mm3/mm/vmscan.c
===================================================================
--- linux-2.6.17-rc4-mm3.orig/mm/vmscan.c	2006-05-24 15:54:19.484968187 -0700
+++ linux-2.6.17-rc4-mm3/mm/vmscan.c	2006-05-25 13:29:03.617251720 -0700
@@ -1652,4 +1652,32 @@ int zone_reclaim(struct zone *zone, gfp_
 		return 0;
 	return __zone_reclaim(zone, gfp_mask, order);
 }
+
+/*
+ * Drop all unmapped pages from the indicated node.
+ */
+void drop_node_pagecache(int node) {
+	struct zone *zone;
+	struct scan_control sc = {
+		.may_writepage = 0,
+		.may_swap = 0,
+		.nr_mapped = read_page_state(nr_mapped),
+		.swap_cluster_max = SWAP_CLUSTER_MAX,
+		.gfp_mask = GFP_USER,
+		.swappiness = vm_swappiness,
+	};
+
+	disable_swap_token();
+	current->flags |= PF_MEMALLOC;
+	for (zone = NODE_DATA(node)->node_zones;
+		zone < NODE_DATA(node)->node_zones + MAX_NR_ZONES;
+		zone++) {
+
+		if (!populated_zone(zone) || zone->all_unreclaimable)
+			continue;
+
+		shrink_zone(0, zone, &sc);
+	}
+	current->flags &= ~PF_MEMALLOC;
+}
 #endif
Index: linux-2.6.17-rc4-mm3/fs/drop_caches.c
===================================================================
--- linux-2.6.17-rc4-mm3.orig/fs/drop_caches.c	2006-05-11 16:31:53.000000000 -0700
+++ linux-2.6.17-rc4-mm3/fs/drop_caches.c	2006-05-24 15:59:43.061583393 -0700
@@ -8,6 +8,7 @@
 #include <linux/writeback.h>
 #include <linux/sysctl.h>
 #include <linux/gfp.h>
+#include <linux/swap.h>
 
 /* A global variable is a bit ugly, but it keeps the code simple */
 int sysctl_drop_caches;
@@ -66,3 +67,20 @@ int drop_caches_sysctl_handler(ctl_table
 	}
 	return 0;
 }
+
+#ifdef CONFIG_NUMA
+int sysctl_drop_node_caches;
+
+int drop_node_caches_sysctl_handler(ctl_table *table, int write,
+	struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
+{
+	proc_dointvec_minmax(table, write, file, buffer, length, ppos);
+
+	if (!node_online(sysctl_drop_node_caches))
+		return -ENODEV;
+
+	drop_node_pagecache(sysctl_drop_node_caches);
+	return 0;
+}
+#endif
+
Index: linux-2.6.17-rc4-mm3/kernel/sysctl.c
===================================================================
--- linux-2.6.17-rc4-mm3.orig/kernel/sysctl.c	2006-05-23 15:10:22.416150348 -0700
+++ linux-2.6.17-rc4-mm3/kernel/sysctl.c	2006-05-24 15:59:35.908706608 -0700
@@ -73,6 +73,7 @@ extern int printk_ratelimit_jiffies;
 extern int printk_ratelimit_burst;
 extern int pid_max_min, pid_max_max;
 extern int sysctl_drop_caches;
+extern int sysctl_drop_node_caches;
 extern int percpu_pagelist_fraction;
 extern int compat_log;
 extern int print_fatal_signals;
@@ -874,6 +875,17 @@ static ctl_table vm_table[] = {
 		.proc_handler	= drop_caches_sysctl_handler,
 		.strategy	= &sysctl_intvec,
 	},
+#ifdef CONFIG_NUMA
+	{
+		.ctl_name	= VM_DROP_NODE_CACHES,
+		.procname	= "drop_node_caches",
+		.data		= &sysctl_drop_node_caches,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= drop_node_caches_sysctl_handler,
+		.strategy	= &sysctl_intvec,
+	},
+#endif
 	{
 		.ctl_name	= VM_MIN_FREE_KBYTES,
 		.procname	= "min_free_kbytes",
Index: linux-2.6.17-rc4-mm3/include/linux/sysctl.h
===================================================================
--- linux-2.6.17-rc4-mm3.orig/include/linux/sysctl.h	2006-05-23 15:10:22.056797601 -0700
+++ linux-2.6.17-rc4-mm3/include/linux/sysctl.h	2006-05-24 15:56:44.819706081 -0700
@@ -194,6 +194,7 @@ enum
 	VM_ZONE_RECLAIM_INTERVAL=32, /* time period to wait after reclaim failure */
 	VM_PANIC_ON_OOM=33,	/* panic at out-of-memory */
 	VM_SWAP_PREFETCH=34,	/* swap prefetch */
+	VM_DROP_NODE_CACHES=35,	/* drop node pagecache */
 };
 
 /* CTL_NET names: */
Index: linux-2.6.17-rc4-mm3/include/linux/mm.h
===================================================================
--- linux-2.6.17-rc4-mm3.orig/include/linux/mm.h	2006-05-24 15:54:33.032956202 -0700
+++ linux-2.6.17-rc4-mm3/include/linux/mm.h	2006-05-24 15:59:22.354859542 -0700
@@ -1110,6 +1110,8 @@ int in_gate_area_no_task(unsigned long a
 
 int drop_caches_sysctl_handler(struct ctl_table *, int, struct file *,
 					void __user *, size_t *, loff_t *);
+int drop_node_caches_sysctl_handler(struct ctl_table *, int, struct file *,
+					void __user *, size_t *, loff_t *);
 unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
 			unsigned long lru_pages);
 void drop_pagecache(void);